Control systems for electrical motors typically include a feedback device such as a position sensor to provide data to measure position and rotational velocity of the motor. On a three-phase multipole synchronous electrical motor, precise and accurate measurement of position of a rotor relative to each of the poles of a stator is important to achieve efficient transmission of electrical energy. Rotor position is typically measured using the position sensor to determine position of the resolver. Position of the resolver relative to the machine rotor is subject to error due to factors including manufacturing variations and tolerances. Electrical motor manufacturers have attempted to correct errors in resolver position measurement using adjustments and post-assembly calibrations. Manufacturers have also attempted to correct sensor-related errors by introducing sensorless techniques for determining rotor position by monitoring and analyzing electromagnetic characteristics of the motor.
Vehicle propulsion systems comprising hybrid powertrains are known for managing the input and output torques of various torque-generative devices, most commonly internal combustion engines and electric machines. One hybrid powertrain architecture comprises a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving torque from a torque-generative source, e.g. an internal combustion engine, and an output member for delivering motive torque from the transmission to a vehicle driveline. Motive torque is transmitted to the transmission from first and second electrical machines operatively connected to an energy storage device for interchanging electrical power therebetween. A controller is provided for regulating the electrical power interchange between the energy storage device and the electrical machines.
The electrical machines preferably comprise known permanent magnet synchronous motor/generator machines, each constructed of a multi-pole electrical stator and a rotor device. Such machines are preferable for powertrain and vehicle applications because they exhibit high torque-to-inertia ratios, high efficiency, and high power density. In such machines, the controller requires accurate and precise information regarding position of the rotor device relative to the stator in order to optimize electrical energy efficiency, thus leading to improved fuel economy.
Prior art systems utilize such techniques as tight machine tolerances and assembly methods, coupled with multiple position sensing devices to ensure accurate measurement of rotor position relative to the stator.
When using PM synchronous machines, absolute position (within one pole pair pitch) is required. Also, the accuracy of this position measurement is critical, as it will affect the performance of the motor control, most noticeably in torque production and linearity. Using a resolver can provide precise position measurement. However, the accuracy of the measurement is directly affected by the initial alignment of the resolver during installation. The installation of the resolver and mechanical alignment can be difficult to control in production.
It is therefore desirable to use a self-aligning start-up algorithm in the motor control.
There is a need to provide an improved method and system to precisely and accurately determine position of a rotor device in a stator for an electrical machine, especially one for application on a fuel/electric hybrid powertrain for a vehicle.